The recent increase in S. pyogenes invasive disease emphasizes the ability of this organism to acquire new survival strategies that allow dissemination and growth in previously uninhabitable sites. Despite enormous research efforts, a clear picture does not exist as to how a disease progresses from a self-limiting superficial infection to the condition of invasive disease, or how S. pyogenes can circumvent the battery of host defense mechanisms in multiple tissues during an invasive infection. In order to identify specific virulence determinants for invasive disease, we have developed an animal model of invasive disease using the zebrafish (Danio rerio). Three mutants with random insertions in separate genes of the salivaricin A lantibiotic locus were identified as being attenuated in the zebrafish invasive disease model. One of these mutants is also deficient in intracellular survival in macrophages. While several mechanisms have been identified for evasion of phagocytosis by S. pyogenes, not much is known about how a typically extracellular pathogen can survive in the intracellular environment. Our long-range goal is to define host-pathogen interactions during an infection that lead to activation of virulence mechanisms and invasive streptococcal disease. The objective of the current application is to characterize the virulence mechanism of a locus in S. pyogenes that allows the pathogen to subvert the innate immune system and cause invasive disease. The central hypothesis of the proposed research is: the function of the S. pyogenes salivaricin locus has evolved from lantibiotic production to a mechanism of virulence and survival during an infection. We plan to test our central hypothesis and accomplish the overall objective of this application by pursuing the following specific aims: 1) identify which proteins encoded by the sal operon are important for virulence;2) identify the mechanism of the SalY permease in virulence;and 3) identify the role of the sal operon in intracellular survival. Collectively, these outcomes will provide new information on how S. pyogenes has evolved to survive elements of the innate immune system and contribute to disease progression as well as identify new targets for antimicrobial therapy. PUBLIC HEALTH RELEVANCE: Streptococcal pathogens are remarkably efficient at causing disease, providing a major challenge to the medical community and an enormous financial burden to our health care system. The research described in this proposal will identify how these pathogens have developed ways in which to avoid the immune system during infection. Confirmation of these mechanisms will have direct relevance to human disease and clinical treatment.